R-410A Application Experience

 

 

D. B. Bivens, J. R. Morley, W.Wells

DuPont Fluoroproducts

 

 

Abstract: R- 410A is attracting a lot of interest among Air Conditioning system manufacturers because of its attractive properties as a refrigerant working fluid. This paper discusses the thermophysical properties of R-410A, highlighting those aspects which contribute to its energy efficiency, as well as those which limit its application range. The results of laboratory testing of R-410A air conditioning systems over a wide range of ambient (condensing temperature) conditions are presented.

 

Background: R-22 has been the life blood of the domestic and commercial air conditioning industry for many decades. When its phase out was signalled by the Copenhagen Amendment to the Montreal Protocol in 1992 the refrigeration/air conditioning industry was fully engaged in introducing alternative technologies for the CFCs (R-11, R-12, R-502, etc.). The publication, in 1994, of the European ODS regulation EC 3093/94 which imposed an earlier (than that of the Montreal Protocol) phase out for the supply of HCFCs (including R-22), and went one step further by imposing a time-table of specific use bans for these substances, accelerated the development of alternatives for R-22. Refrigerant manufacturers had been developing alternatives for R-22 focusing on those substances which mirrored as closely as possible the thermo-physical, chemical stability and safety characteristics of R-22, within, obviously the constraints imposed by ODS regulation.

The industry (refrigerant manufacturers and air conditioning system OEMs) initially settled on R-407C as being the preferred replacement for R-22 for air conditioning. However R-407C, being a zeotropic mixture with a significant temperature glide, is not suitable for all (specifically certain chiller) air conditioning applications. The continuing emphasis on system energy efficiency provoked the industry to continue researching other HFC fluids, and this led to the development of R-410A. R-410A is not a like-for-like replacement for R-22 because it is a much higher pressure fluid (and also has a significantly higher volumetric refrigeration capacity) than R-22 and thus cannot be used in refrigeration equipment rated for R-22 (without re-rating, if this is possible).

Figure 1 shows the relative pressure (at 55C) and typical volumetric refrigeration capacity relative to R-22.

 

 


Fig.1 Comparison of R-22 and R-410A

 


Initial trials of R-410A showed that air conditioning systems using this fluid exhibited an energy efficiency superior to that in comparable, un-optimised, systems using R-407C or R-22.

 

R-410A: R-410A is a near-azeotropic mixture of HFC-32 and HFC-125. It has a very low temperature glide (around 0.1K), however it is truly zeotropic over its useable temperature range the composition of its vapour in equilibrium with the liquid at any temperature (below the Critical Point) is different from the composition of the liquid phase. This means that, although R-410A has a very low temperature glide it should not be handled as an azeotropic fluid: transfers should always be made from the liquid phase. One potential draw-back with regard to the applications of R-410A is that its Critical Temperature is significantly lower than that of R-407C or R-22 (see table 1)

 

 

 

Table 1 Physical Property Comparison

 

 

R-22

R-407C

R-410A

Critical Temperature (C)

96.2

86.1

72.0

Critical Pressure (Bar a)

49.9

46.3

47.7

Saturation Pressure at 50C (bar a)

19.4

22.1

30.6

 

 

An analysis of the theoretical refrigeration cycle shows that the theoretical cycle efficiency (COP) of R410A is significantly LESS than that of R-22 by around 4 6%. This is in disagreement with the early laboratory trials of R-410A in air conditioning systems which showed a significant INCREASE in COP vs. R-22. The apparent anomalous behaviour of R-410A has been shown to be due to its very favourable (opposite R-22, or R-407C, for that matter) transport properties. See Tables 2 and 3

 

Table 2 Transport Property Comparison

Saturated Liquid (10C)

 

 

R-22

R-410A

Density (kg/cu.m.)

1247

1130

Viscosity (Pa.S)

196

147

Thermal Conductivity (W/m.K)

0.090

0.108

 

 

 

 

 

Table 3 Transport Property Comparison

Saturated Vapour (10C)

 

 

R-22

R-410A

Density (kg/cu.m.)

28.8

41.8

Viscosity (Pa.S)

12.0

12.9

Thermal Conductivity (W/m.K)

0.0101

0.0136

 

 

These differences in transport properties result in reduced viscous losses (i.e. pressure drop) in the system and within the compressor itself, and also give improved heat transfer characteristics in the evaporator and condenser. Thus the improved energy efficiency of R-410A systems over R-22 systems under normal air conditioning conditions.

Performance of R-410A in high temperature condensing ambients:

As discussed previously R-410A has a relatively low Critical Temperature. This will impact its performance in conditions where high condensing temperatures are required in air condensing systems in hot climates, in heat pump applications, etc.

To evaluate the impact of condensing ambient temperatures on system performance a series of performance tests were undertaken in controlled laboratory conditions using several commercial R-410A system configurations for air conditioning.

The results of these tests are presented below as performance relative to the performance at 35C Ambient for each refrigerant fluid, in order to discount absolute differences in performance between R-22 and R-410A. In general there was an approximately 15C approach temperature at the condenser (the difference between the condensing temperature and the temperature of the condensing ambient). The performance of both R-22 and R-410A is influenced by condensing temperature R410A is slightly more sensitive to condensing ambient temperature than is R-22 up to around 45C. Above this temperature (equivalent to a condensing temperature of around 60C) the refrigeration capacity of the R-410A system starts to fall off more rapidly. At this temperature the relative drop in capacity exhibited by R-410A systems is around 10% greater than that of an R-22 system.

 

These results are summarised in Figure 1 and Figure 2:

 

 


Fig.1

 

 

 



Fig. 2

 


The effect of condensing ambient temperature is system dependent. Figure 3 compares a Window unit and a ducted split system

 


Fig 3

 

 


Conclusions: Trials with R-410A under varying condensing conditions demonstrate that its performance (capacity and energy efficiency) does decrease with condensing temperature in a manner somewhat similar to that of R-22, and there are no abrupt changes as the condensing temperature reaches and passes the Critical Temperature. (This will be at condensing ambient temperatures of around 55 60C.) The system capacity at the Critical Temperature is around 60 70% of that 35C (around a 10% greater drop than R-22 experiences over the same temperature range). The rate of performance reduction with increasing condensing temperature is a function of system design.